A. Field of the Invention
The present invention relates to a variable camber airfoil, and more particularly to an apparatus particularly adatped to vary the camber of the trailing edge portion of an airfoil.
B. Brief Description of the Prior Art
A common way of modifying the lift characteristics of an airfoil for low speed operation is to use leading edge and trailing edge devices which either pivot or slide outwardly from the airfoil to a deployed position. With many such devices, there is the problem that during deployment, there is an interruption in smooth air flow over the airfoil. Also, many of these devices are not able to be deployed to intermediate positions while maintaining the proper flow of air over the airfoil.
Accordingly, there have appeared in the prior art various devices to vary the shape of the airfoil itself in a manner to change the camber and thus modify its lift characteristics. One common method employed in the prior art is to pivotally mount the trailing edge section of the airfoil in some manner to the main structure of the wing. Typical of such devices are those shown in the following patents: U.S. Pat. No. 1,710,672, Bonney; U.S. Pat. No. 1,710,673, Bonney; U.S. Pat. No. 1,766,107, Cook, Jr.; U.S. Pat. No. 1,813,485, Cook, Jr.; U.S. Pat. No. 2,650,075, Carhart et al.; and French patent No. 574,500.
Another approach to vary the camber of the wing is shown in two patents issued to Antoni, U.S. Pat. No. 1,690,765 and U.S. Pat. No. 1,886,362. In these patents, forward and rear sections of the airfoil are connected to one another so that relative angular rotation of the two sections causes them to flex the wing in a curved configuration.
Another means of accomplishing the cambering of an airfoil is shown in U.S. Pat. No. 1,828,981, Parker, where the lower skin of the airfoil is connected to a plurality of pivotally mounted links, the angular positions of which are offset with respect to one another. Rotation of these links causes the middle portion of the lower skin to deflect upwardly, while the trailing edge portion of the airfoil is deflected downwardly.
U.S. Pat. No. 2,022,806, Grant, shows another mechanism for changing the camber along substantially the entire chord length of the airfoil by providing the airfoil with a supporting framework made up of a plurality of triangular trusses, the lower ends of which can be moved relative to each other. By moving the lower ends of the trusses either closer or further away from one another, the length of the lower skin of the wing can be changed with respect to the length of the upper skin, so as to cause a corresponding change in the camber of the wing.
Another approach is shown in U.S. Pat. No. 1,585,586, Hewitt, where the lower skin of an airfoil is connected at its forward end to a movable member. A simple actuator moves the movable member forwardly to pull the lower skin forwardly relative to the upper skin and thus cause the airfoil to assume a more curved configuration. U.S. Pat. No. 3,332,383, Wright, shows a variable camber airfoil where forward and rear mounting sections are pivotally connected one to another. Relative rotation of these two mounting sections causes the airfoil to assume a cambered configuration.
U.S. Pat. No. 1,823,069, Stroop, shows a device utilizing elongate actuating members which extend into the trailing edge, these actuating members tapering toward the trailing edge in a curved configuration. By rotating these curved members about their axial lengths, the outer curved tips thereof move upwardly or downwardly to change the camber of the airfoil. This same general concept appears in U.S. Pat. No. 3,109,613, Bryant et al., where there are a plurality of rotatable members extending into the trailing edge portion of the airfoil, with each rearwardly positioned member having an increased angular deviation from a straight line axis. By rotating these sets of members in unison, the airfoil is caused to assume a curved configuration.
U.S. Pat. No. 1,412,455, Crowell et al., shows an airfoil having a plurality of cam members mounted for rotation about horizontal axes which cause the lower skin section to move upwardly or downwardly. U.S. Pat. No. 2,484,687, Carl, Jr., shows a cable operated device to deflect the rear portion of a sail for a boat.
U.S. Pat. No. 3,698,668, Cole, shows a device for deflecting an edge portion of an airfoil by means of a mechanism made up of a plurality of canted hinges positioned in the variable camber section of the airfoil. These hinges are mounted about vertical axes, and rotation of the hinge members causes a shortening of the lower airfoil portion to cause it to curve.
U.S. Pat. No. 3,941,344, Cole, shows several different mechanisms for delfecting both the leading and trailing edges of an airfoil. In general these devices comprise a rib beam or the like which extends into the cambered section, with this rib beam being deflected upwardly or downwardly to change the camber. The rib beam has associated linkage to deflect the extreme outer portion of the cambered section to an angle greater than the deflection of the rib beam itself.
While the prior art has provided devices which are operable to change the camber of an airfoil, there is still a continuing need to seek improvements with regard to simplicity and reliability of structure and operation, and also to accomplish the change of camber so that the airfoil, particularly with regard to its upper surface, is always in a smooth continuous curve with no significant surface discontinuities to induce flow separation.